President Omar al-Bashir has called the Janjaweed "thieves and gangsters".

But refugees say air raids by government aircraft would be followed by attacks from the Janjaweed, who would ride into villages on horses and camels, slaughtering men, raping women and stealing whatever they could find.

The US and some human rights groups have said genocide is taking place - though a UN investigation team in 2005 concluded that war crimes had been committed but there had been no intent to commit genocide.

Trials have been announced in Khartoum of some members of the security forces suspected of abuses - but this is viewed as part of a campaign against attempts to get suspects tried at the International Criminal Court (ICC) in The Hague.

What has happened to Darfur's civilians?

The United Nations says more than 2.7 million people have fled their homes and now live in camps near Darfur's main towns.

Darfuris say the Janjaweed patrol outside the camps and men are killed and women raped if they venture too far in search of firewood or water.

Some 200,000 people have also sought safety in neighbouring Chad. Many of these are camped along a 600km (372 mile) stretch of the border and remain vulnerable to attacks from the Sudan side.

Chad's eastern areas have a similar ethnic make-up to Darfur and the violence has spilled over the border area, with the neighbours accusing one another of supporting each other's rebel groups.

Many aid agencies have been working in Darfur but they are unable to get access to vast areas because of the insecurity.

Several were banned from northern Sudan after the International Criminal Court issued an arrest warrant for President Bashir in 2009 for alleged war crimes.

How many have died?

The United Nations says up to 300,000 people have died from the combined effects of war, hunger and disease.

Janjaweed gunmen are accused of prowling outside refugee camps

President Bashir puts the death toll at 10,000.

Accurate figures are difficult to research and have made no distinction between those dying as a result of violence and those dying as a result of starvation or disease in the camps.

The numbers are crucial in determining whether the deaths in Darfur are genocide or - as the Sudanese government says - the situation is being exaggerated.

Is anyone trying to stop the fighting?

Yes.

There are thousands of peacekeepers in the region under the auspices of a joint African Union-UN peacekeeping mission, Unamid.

Last August, the UN's outgoing military commander General Martin Agwai said the conflict was effectively over and isolated attacks and banditry were the region's main problems now.

There was a peace deal in 2006, but only one of many rebel factions signed up to it.

Qatar, the United Nations, the African Union, Arab League and Chad have all helped to arrange peace talks between Khartoum and Jem over the past few years.

The US envoy to Darfur, Scott Gration, has also been involved in talks aimed at getting the rebel groups to agree a common position so they can take part in broader peace talks.

It is hoped that the ceasefire with Jem will see other rebels sit down at the negotiating table.

Who is to blame?

The international community lays much of the blame on Mr Bashir.

Omar al-Bashir says ICC charges reflect Western hostility to Sudan

He has frequently been accused of supporting the pro-government militias.

The International Criminal Court in The Hague issued an arrest warrant last year for war crimes and crimes against humanity.

An attempt to add genocide to the charge was initially refused - but prosecutors appealed and the court's pre-trial chamber has now been ordered to reconsider genocide charges.

Rebel groups have also been held responsible for some atrocities.

But the case against rebel leader Bahar Idriss Abu Garda, accused of planning the killing of 12 African Union peacekeepers in 2007, was dropped this year as the ICC ruled there was not enough evidence to support a trial.

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